Activation of UCP2 by anethole trithione suppresses neuroinflammation after intracerebral hemorrhage

Succinate Activates Uncoupling Protein 2 to Suppress Neuroinflammation and Confer Protection Following Intracerebral Hemorrhage

Aims: Succinate, a metabolite in the tricarboxylic acid cycle, is increasingly recognized to play essential roles in inflammation by functioning either as an intracellular or extracellular signaling molecule. However, the role and mechanisms of succinate in inflammation remain elusive. Here, we investigated the mechanism underlying the effects of succinate on neuroinflammation in intracerebral hemorrhage (ICH) models. Results: We unexpectedly found that succinate robustly inhibited neuroinflammation and conferred protection following ICH. Mechanistically, the oxidation of succinate by succinate dehydrogenase (SDH) drove reverse electron transport (RET) at mitochondrial complex I, leading to mitochondrial superoxide production in microglia. Complex I-derived superoxides, in turn, activated uncoupling protein 2 (UCP2). By using mice with specific deletion of UCP2 in microglia/macrophages, we showed that UCP2 was needed for succinate to inhibit neuroinflammation, confer protection, and activate downstream 5'-adenosine monophosphate-activated protein kinase (AMPK) following ICH. Moreover, knockdown of SDH, complex I, or AMPK abolished the therapeutic effects of succinate following ICH. Innovation and Conclusion: We provide evidence that driving complex I RET to activate UCP2 is a novel mechanism of succinate-mediated intracellular signaling and a mechanism underlying the inhibition of neuroinflammation by succinate.

Aspartame-induced cognitive dysfunction: Unveiling role of microglia-mediated neuroinflammation and molecular remediation

Aspartame, an artificial sweetener, is consumed by millions of people globally. There are multiple reports of aspartame and its metabolites affecting cognitive functions in animal models and humans, which include learning problems, headaches, seizures, migraines, irritable moods, anxiety, depression, and insomnia. These cognitive deficits and associated symptoms are partly attributed to dysregulated excitatory and inhibitory neurotransmitter balance due to aspartate released from aspartame, resulting in an excitotoxic effect in neurons, leading to neuronal damage. However, microglia, a central immunocompetent cell type in brain tissue and a significant player in inflammation can contribute to the impact. Microglia rapidly respond to changes in CNS homeostasis. Aspartame consumption might affect the microglia phenotype directly via methanol-induced toxic effects and indirectly via aspartic acid-mediated excitotoxicity, exacerbating symptoms of cognitive decline. Long-term oral consumption of aspartame thus might change microglia's phenotype from ramified to activated, resulting in chronic or sustained activation, releasing excess pro-inflammatory molecules. This pro-inflammatory surge might lead to the degeneration of healthy neurons and other glial cells, impairing cognition. This review will deliberate on possible links and research gaps that need to be explored concerning aspartame consumption, ecotoxicity and microglia-mediated inflammatory cognitive impairment. The study covers a comprehensive analysis of the impact of aspartame consumption on cognitive function, considering both direct and indirect effects, including the involvement of microglia-mediated neuroinflammation. We also propose a novel intervention strategy involving tryptophan supplementation to mitigate cognitive decline symptoms in individuals with prolonged aspartame consumption, providing a potential solution to address the adverse effects of aspartame on cognitive function.

Regulators of phagocytosis as pharmacologic targets for stroke treatment

Stroke, including ischemic and hemorrhagic stroke, causes massive cell death in the brain, which is followed by secondary inflammatory injury initiated by disease-associated molecular patterns released from dead cells. Phagocytosis, a cellular process of engulfment and digestion of dead cells, promotes the resolution of inflammation and repair following stroke. However, professional or non-professional phagocytes also phagocytose stressed but viable cells in the brain or excessively phagocytose myelin sheaths or prune synapses, consequently exacerbating brain injury and impairing repair following stroke. Phagocytosis includes the smell, eating and digestion phases. Notably, efficient phagocytosis critically depends on phagocyte capacity to take up dead cells continually due to the limited number of phagocytes vs. dead cells after injury. Moreover, phenotypic polarization of phagocytes occurring after phagocytosis is also essential to the proresolving and prorepair properties of phagocytosis. Much has been learned about the molecular signals and regulatory mechanisms governing the sense and recognition of dead cells by phagocytes during the smell and eating phase following stroke. However, some key areas remain extremely understudied, including the mechanisms involved in digestion regulation, continual phagocytosis and phagocytosis-induced phenotypic switching following stroke. Here, we summarize new discoveries related to the molecular mechanisms and multifaceted effects of phagocytosis on brain injury and repair following stroke and highlight the knowledge gaps in poststroke phagocytosis. We suggest that advancing the understanding of poststroke phagocytosis will help identify more biological targets for stroke treatment.

Pazopanib alleviates neuroinflammation and protects dopaminergic neurons in LPS-stimulated mouse model by inhibiting MEK4-JNK-AP-1 pathway

Parkinson's disease (PD) is a progressive neurodegenerative disease characterized by the loss of dopaminergic (DA) neurons and the accumulation of Lewy bodies (LB) in the substantia nigra (SN). Evidence shows that microglia-mediated neuroinflammation plays a key role in PD pathogenesis. Using TNF-α as an indicator for microglial activation, we established a cellular model to screen compounds that could inhibit neuroinflammation. From 2471 compounds in a small molecular compound library composed of FDA-approved drugs, we found 77 candidates with a significant anti-inflammatory effect. In this study, we further characterized pazopanib, a pan-VEGF receptor tyrosine kinase inhibitor (that was approved by the FDA for the treatment of advanced renal cell carcinoma and advanced soft tissue sarcoma). We showed that pretreatment with pazopanib (1, 5, 10 μM) dose-dependently suppressed LPS-induced BV2 cell activation evidenced by inhibiting the transcription of proinflammatory factors iNOS, COX2, Il-1β, and Il-6 through the MEK4-JNK-AP-1 pathway. The conditioned medium from LPS-treated microglia caused mouse DA neuronal MES23.5 cell damage, which was greatly attenuated by pretreatment of the microglia with pazopanib. We established an LPS-stimulated mouse model by stereotactic injection of LPS into mouse substantia nigra. Administration of pazopanib (10 mg·kg-1·d-1, i.p., for 10 days) exerted significant anti-inflammatory and neuronal protective effects, and improved motor abilities impaired by LPS in the mice. Together, we discover a promising candidate compound for anti-neuroinflammation and provide a potential repositioning of pazopanib in the treatment of PD.

Necroptotic kinases are involved in the reduction of depression-induced astrocytes and fluoxetine's inhibitory effects on necroptotic kinases

The role of astrocytes in major depressive disorder has received great attention. Increasing evidence indicates that decreased astrocyte numbers in the hippocampus may be associated with depression, but the role of necroptosis in depression is unknown. Here, in a chronic unpredictable mild stress (CUMS) mouse model and a corticosterone (Cort)-induced human astrocyte injury model in vitro, we found that mice treated with chronic unpredictable mild stress for 3-5 weeks presented depressive-like behaviors and reduced body weight gain, accompanied by a reduction in astrocytes and a decrease in astrocytic brain-derived neurotropic factors (BDNF), by activation of necroptotic kinases, including RIPK1 (receptor-interacting protein kinase 1)/p-RIPK1, RIPK3 (receptor-interacting protein kinase 3)/p-RIPK3 and MLKL (mixed lineage kinase domain-like protein)/p-MLKL, and by upregulation of inflammatory cytokines in astrocytes of the mouse hippocampus. In contrast, necroptotic kinase inhibitors suppressed Cort-induced necroptotic kinase activation, reduced astrocytes, astrocytic necroptosis and dysfunction, and decreased Cort-mediated inflammatory cytokines in astrocytes. Treatment with fluoxetine (FLX) for 5 weeks improved chronic unpredictable mild stress-induced mouse depressive-like behaviors; simultaneously, fluoxetine inhibited depression-induced necroptotic kinase activation, reversed the reduction in astrocytes and astrocytic necroptosis and dysfunction, decreased inflammatory cytokines and upregulated brain-derived neurotropic factors and 5-HT1A levels. Furthermore, fluoxetine had no direct inhibitory effect on receptor-interacting protein kinase 1 phosphorylation. The combined administration of fluoxetine and necroptotic kinase inhibitors further reduced corticosterone-induced astrocyte injury. In conclusion, the reduction in astrocytes caused by depressive-like models in vivo and in vitro may be associated with the activation of necroptotic kinases and astrocytic necroptosis, and fluoxetine exerts an antidepressive effect by indirectly inhibiting receptor-interacting protein kinase 1-mediated astrocytic necroptosis.

Ulinastatin alleviates early brain injury after intracerebral hemorrhage by inhibiting oxidative stress and neuroinflammation via ROS/MAPK/Nrf2 signaling pathway

Purpose:

Spontaneous intracerebral hemorrhage (ICH) is still a major public health problem, with high mortality and disability. Ulinastatin (UTI) was purified from human urine and has been reported to be anti-inflammatory, organ protective, and antioxidative stress. However, the neuroprotection of UTI in ICH has not been confirmed, and the potential mechanism is unclear. In the present study, we aimed to investigate the neuroprotection and potential molecular mechanisms of UTI in ICH-induced early brain injury in a C57BL/6 mouse model.

Methods:

The neurological score, brain water content, neuroinflammatory cytokine levels, oxidative stress levels, and neuronal damage were evaluated.

Results:

UTI treatment markedly increased the neurological score, alleviated brain edema, decreased the levels of the inflammatory cytokines tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), IL-6, and NF-κB, decreased the levels of reactive oxygen species (ROS) and malondialdehyde (MDA), and upregulated the levels of glutathione (GSH), superoxide dismutase (SOD), and Nrf2. This finding indicated that UTI-mediated inhibition of neuroinflammation and oxidative stress alleviated neuronal damage after ICH. The neuroprotective capacity of UTI is partly dependent on the ROS/MAPK/Nrf2 signaling pathway.

Conclusions:

UTI improves neurological outcomes in mice and reduces neuronal death by protecting against neural neuroinflammation and oxidative stress.

Lipoxin A4 Receptor Stimulation Attenuates Neuroinflammation in a Mouse Model of Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) is caused by the rupture of blood vessels in the brain. The excessive activation of glial cells and the infiltration of numerous inflammatory cells are observed during bleeding. Thrombin is a key molecule that triggers neuroinflammation in the ICH brain. In this study, we focused on lipoxin A₄ (LXA₄), an arachidonic acid metabolite that has been reported to suppress inflammation and cell migration. LXA₄ and BML-111, an agonist of the LXA₄ receptor/formyl peptide receptor 2 (ALX/FPR2), suppressed microglial activation; LXA₄ strongly inhibited the migration of neutrophil-like cells in vitro. ALX/FPR2 was expressed on neutrophils in the ICH mouse brain and the daily administration of BML-111 attenuated the motor coordination dysfunction and suppressed the production of proinflammatory cytokines in the ICH mouse brain. On the other hand, BML-111 did not show a significant reduction in the number of microglia and neutrophils. These results suggest that systemic administration of ALX/FPR2 agonists may suppress the neuroinflammatory response of microglia and neutrophils without a change in cell numbers. Additionally, their combination with molecules that reduce cell numbers, such as modulators of leukotriene B₄ signaling, may be required in future studies.

Neuroprotective Potential of Mild Uncoupling in Mitochondria. Pros and Cons

There has been an explosion of interest in the use of uncouplers of oxidative phosphorylation in mitochondria in the treatment of several pathologies, including neurological ones. In this review, we analyzed all the mechanisms associated with mitochondrial uncoupling and the metabolic and signaling cascades triggered by uncouplers. We provide a full set of positive and negative effects that should be taken into account when using uncouplers in experiments and clinical practice.